1. Field of the Invention
The present invention relates to a method of easily measuring the inner diameter of a pipe such as a gas pipe buried underground within a short period of time.
2. Description of the Relevant Arts
Known conventional methods of measuring the inner diameter of a gas pipe buried underground and inspecting whether a foreign substance such as earth and sand enters into piping include a method of inserting an inspection camera into the pipe to pick up the internal state of the pipe and observe the resultant image, thereby determining the internal state, or using an elastically deformable probe and inserting the probe into the pipe to detect the deformed state of the probe, thereby measuring the inner diameter of the pipe (Japanese Patent Publication No. SHO 57-34482) and a method of radiating a laser beam on the inner wall surface of a pipe and receiving a beam reflected by the inner wall surface to measure the inner diameter (Japanese Patent Laid-Open No. HEI 3-261806).
In the above methods, it is difficult to insert the camera, the probe, and an apparatus for radiating the laser beam and receiving the reflected beam in the pipe so as to conform to the complicated bent shape of the pipe, and the internal state of the pipe cannot be properly inspected. In addition, an insertion hole is required to insert the above inspecting means. To inspect the buried pipe, cumbersome, time-consuming construction work such as digging is be involved. In addition, the inspection distance per cycle is limited to the length of a cable or the like connected to the camera or probe. When inspection is required for a long distance, the number of inspection cycles are undesirably increased, requiring much labor and high cost.